In a known attachment structure of an oil control valve disclosed in JP2006-29166A (Reference 1), a metal sleeve (corresponding to a valve body and a sleeve of this disclosure) and a resin valve casing (corresponding to a cover of this disclosure) are integrally insert-molded and attached to each other. More particularly, a primer is applied on an outer peripheral surface of the metal sleeve before the insert-molding operation so that the metal sleeve is attached to a resin material that forms the valve casing.
However, in the attachment structure of the oil control valve (corresponding to a solenoid valve of this disclosure) disclosed in the Reference 1, no countermeasure is disclosed against heat deformation that may occur due to a difference in thermal expansion coefficients between different materials, for example, the materials of the metal sleeve and the resin valve casing. Thus, when the metal sleeve and the resin valve casing are integrally insert-molded, the resin cover may be thermally deformed or deteriorate due to heat of a fluid or heat conducted from an internal combustion engine, thereby causing a gap between the sleeve and the valve casing, which may result in unintentional fluid communication between two oil holes (corresponding to two fluid passages of this disclosure). Particularly, when the difference in the thermal expansion coefficient between the different materials exists, for example, the metal sleeve and the resin valve casing, the resin valve casing may come apart from the metal sleeve, and thus the unintentional fluid communication between the two oil holes may be established.
A need thus exists for a structure of a solenoid valve attached to a resin cover by insert-molding, which is not susceptible to the drawback mentioned above.